Quiz #4
1. DNA SUPERCOILING
Write out the equation that describes linking number, defining each variable.
Lk= Tw + Wr
Lk = total # of times that strands cross
Wr= # of times that the double helix crosses itself
Wr= # of times that the strands cross, but excluding writhe
2.RECOMBINATION
Draw out the pathway of recBCD homologous recombination
Details on slides
3. Define or describe the following
Ac/Ds: Ac/Ds are transposons which were first discovered in maize. Ds is
dissociation locus causes chromosome breakage. Ac is activator and helps Ds
mobilize. The mobility of Ds depends on Ac
Transposase An protein encoded by transposons. It catalyzes cut and paste
reactions of transposons.
NHEJ: Non-homologous ending joining. It is a repair pathway for double-strand
breaks and ligates 2 non-homologous strands together. This pathway is prone to
errors
Footprint: Some transposons leave short, direct repeats behind genomic DNA
when they leave. These short, direct repeats are called “footprint”. They are a
part of genomic DNA.
4. McClintock discovered transposable elements in
maize
plants.
Ds
Was an element that she investigated early on, and found that it
caused chromosome breakage
5. Repair of doble-strand breaks in plant nuclear DNA is mostly by
a. homologous recombination with the unbroken chromosome.
b. non-homologous end joining
c. degrading the broken chromosome and replicating the unbroken homologue
d. Both a and b, with a>b
e. Bother a and b, with b>a
6. How transposons leave a footprint behind genomic DNA.